1. Field of Invention
The invention relates to a pump and an inkjet printer having the pump.
2. Description of Related Art
Inkjet printers eject ink drops from nozzles formed on inkjet heads by making use of various principles to print desired images on sheets, which are recording media. The inkjet heads are connected via tubes to ink tanks, which are ink sources. During printing, ink is sucked from the ink tanks using the capillary action of the nozzles and negative pressure generated by ejecting ink drops from the nozzles. However, when bubbles are trapped in the ink, it is tough to suck the ink from the ink tanks. As such, images cannot be printed on sheets using the inkjet heads.
An inkjet printer disclosed in Japanese Patent Publication No. 7-80304 (pp. 3-5, FIG. 1) can solve such a problem. This printer is provided with a pump for purging, and inkjet heads (recording heads) and ink tanks (ink cartridges) each containing ink that is communicated via flexible tubes inserted through the pump. The pump has a rotor rotatably attached inside to which three rollers are disposed on the circumference of the rotor. The rollers are placed away from each other at equivalent angles and are rotatably supported via respective shafts. In addition, the flexible tubes are disposed between the outside diameter of the rotor and the inside diameter of a circular hollow in the pump. During printing in such a printer, the rollers of the rotor are disposed so that they do not crush the tubes, and ink is sucked from the ink tanks via the tubes to the inkjet heads by the capillary action of the nozzles and negative pressure generated by ejecting ink drops from the nozzles as described above. Then, ink drops are ejected from the nozzles of the inkjet heads, and images are thereby printed on sheets. For a purging operation, the rotor of the pump is rotated so that ink is forcibly supplied from the pump to the inkjet heads. As this rotation enables ink containing bubbles to be eliminated from the inkjet heads, the reliability of the ink supply state can be recovered.
However, in the inkjet printer disclosed in Japanese Patent Publication No. 7-80304, when ink is forcibly supplied to the inkjet heads, the rotor crushes the flexible tubes at a position where the rotor contacts the flexible tubes when the rotor rotates. As a result, there is a problem in that the tubes disposed in the pump are damaged, and the ink supply to the inkjet heads fails.
There also exists a Cary's rotary pump, as a kind of rotary pump, as shown in FIG. 1. The pump 1070 has a case 1073 where a suction inlet 1071 and an exhaust outlet 1072 are formed and a rotor 1074 is rotatably provided so as to make contact with an inner surface of an upper portion of the case 1073 between the suction inlet 1071 and the exhaust outlet 1072. The rotor 1074 is provided at an eccentric position in the case 1073. Two vanes 1076a, 1076b connected by a spring 1075 are disposed in the rotor 1074 so as to slide in a direction of the diameter of the rotor 1074. When the rotor 1074 rotates, the two vanes 1076a, 1076b rotate while making contact with the inner surface of the case 1073 by a spring force and a centrifugal force generated by rotating the rotor 1074.
In the pump 1070 as described, when the rotor 1074, which is located at the eccentric position, rotates, the volume gradually expands in a chamber communicating with the suction inlet 1071 (i.e., chamber 1077a in FIG. 1), and fluid (liquid or gas) is sucked through the suction inlet 1071 therein to with the expansion of the volume. The chamber where the fluid is sucked then shifts to a position that is out of communication with the suction inlet 1071 and the exhaust outlet 1072 (i.e., chamber 1077b in FIG. 1) by rotating the rotor 1074. The chamber then moves to a position in communication with the exhaust outlet 1072 (i.e., chamber 1077c in FIG. 1), where the volume is gradually decreased and the fluid is conveyed through the exhaust outlet 1072 with the decrease of the volume.
The above-described Cary's pump is disclosed in the following document: “27.13 Cary's rotary pump 1” in “Shin kikai no moto 10 pan 1977” [New Fundamentals of Machine 10th edition, 1977]. ed. Kikai no moto fukkan iinkai [Committee for republish of Fundamentals of Machine]. Rikogakusha Publishing Co., Ltd. p 203.